Hitherto, various radar apparatuses have been proposed which are disposed, for example, in front portions of automobiles, and which transmit transmission waves to a predetermined detection area including a region in front of the automobile, and receives waves reflected by a target in the detection area, to thereby detect the target. As one example of such radar apparatuses, the FMCW type is widely employed in the field of automobiles.
The FMCW-type radar apparatus employs a transmission signal having a frequency changing in the form of, e.g., a triangular wave, which alternately includes an up-modulation zone where the frequency of the transmission signal gradually increases, and a down-modulation zone where the frequency of the transmission signal gradually decreases. That type of radar apparatus includes a voltage control oscillator. The frequency of the transmission signal is modulated by varying the frequency of a signal output from the voltage control oscillator. Therefore, an accurate modulated signal in the triangular-wave form can be transmitted by accurately applying a voltage that controls the voltage control oscillator.
To overcome such a problem, in an apparatus described in Patent Document 1, a transmission signal is divided in a predetermined number of division points and a voltage applied to a voltage control oscillator is sequentially corrected and set at each of the division points such that a distance measured at each of the division points matches with a preset desired distance.
Further, in an apparatus described in Patent Document 2, a frequency modulation zone is time-divided into a plurality of short zones, and an FFT process is executed for each of the divided short zones. Then, a voltage applied to a voltage control oscillator is corrected and set by comparing respective frequency spectra of beat signals obtained in the divided short zones and controlling the voltage such that the frequency spectra match with each other.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 8-304532
Patent Document 2: Japanese Unexamined Patent Application Publication No. 11-271428
With the apparatus described in Patent Document 1, however, unless the distance measured at each of the division points is accurate, it is difficult to accurately perform the correction. Obtaining the accurate measured distance requires the measurement and the correction to be repeated in a considerable number of times.
With the apparatus described in Patent Document 2, because the FFT process has to be executed for each of the divided short zones, a processing load is increased. In addition, because the FFT process executed in the short zone on the time basis deteriorates frequency resolution, the measurement and the correction cannot be accurately performed.